Loading docks are frequently equipped with manual or hydraulically operated dockboards that act to bridge the gap and height difference between the dock and the bed of a truck to enable material handling equipment, such as a forklift truck, to move between the dock and the truck bed. One common form of dockboard is mounted in a pit or recess formed in the dock surface and includes a ramp or deckplate which is stored in a generally horizontal position flush with the upper surface of the dock and is movable to an upwardly inclined position. A lip is hinged to the forward edge of the ramp and can be pivoted between a downwardly hanging pendant position, an extended position where the lip forms an extension to the ramp.
Another less expensive type of dockboard is what is commonly referred to as an edge-of-dock type. With this type of dockboard, no pit or recess is required in the loading dock and the dockboard is mounted on the front vertical face of the dock.
A conventional edge-of-dock dockboard includes a center plate having its inner end hinged to the loading dock, and a lip is hinged to the outer end of the center plate. In the storage position, the center plate is positioned horizontally and extends outwardly from the dock, while the lip is in a downwardly hanging or pendant position and is located between the bumpers which are mounted on the front face of the dock.
In operation of a coventional edge-of-dock dockboard, a truck backs toward the dock into engagement with the bumpers, and an operator, standing on the dock and using a long, hook-like implement, engages the center plate and pivots it to the vertical position. The lip is then engaged by the hook and pivoted to the extended vertical position. The dockboard is then lowered to bring the extended lip into engagement with the truck bed.
Because of the weight of the center plate and the lip, it is very difficult to pivot the center plate and the lip upwardly to the vertical position.
Attempts have been made in the past to provide a counterbalancing mechanism for the edge-of-dock dockboard to reduce the amount of manual effort required to pivot the dockboard to its vertical position, but such counterbalancing mechanisms have not been entirely successful. If the counterbalance is applied only to the center plate, the entire weight of the lip must be lifted manually. On the other hand, if the counterbalance is applied to the lip, the lip may not properly extend and the lip may tend to bounce or jack-knife when in the extended position as a load travels across the dockboard. Because of this, there has been a need for a counterbalancing system that will partially counterbalance the weight of both the center plate and the lip and will also aid in maintaining the lip in an extended position.